1. Field of the Invention
The present invention relates to an image recording device, in which, while a printing plate precursor wound around a peripheral surface of a rotating support is being rotated, a recording head is moved in an axial direction of the rotating support, so as to scan-record an image.
2. Description of the Related Art
In recent years, technology has been developed for printing plate precursors in an exposure device for directly recording an image using a laser beam or the like on a sheet-type recording material, especially on a photosensitive layer (emulsion surface) on a support of a printing plate precursor. This technology has enabled rapid image-recording on a printing plate precursor.
In an automatic exposure device which uses image-recording technology on a printing plate precursor, a rotary drum, around whose peripheral surface a printing plate precursor is wound, is rapidly rotated (main scanning) while a recording head (exposure head) is moved in an axial direction of the rotary drum (sub-scanning). Images are thus recorded onto printing plate precursors.
The recording head is generally moved using a ball screw mechanism. The ball screw mechanism comprises a shaft having a threaded outer surface, and a moving block into which the shaft is screwed and which is prevented from rotating axially. The recording head is mounted on a fixed stage to the moving block, and thus moved.
The ball screw mechanism, the rotary drum and the printing plate precursor expand or contract due to temperature changes in the device. When a material of components of the ball screw mechanism differs from that of the rotary drum and/or the support of the printing plate precursor, the materials have coefficients of thermal expansion, which are different from each other; thus, the amounts of expansion/contraction due to temperature changes are different from each other. Accordingly, a problem arises in that the relative positions between the ball screw mechanism and the printing plate precursor deviate from each other, whereby an image-recording start position in the sub-scanning direction is deviated from, resulting in an improperly formed image.
A moving speed of the recording head during driving is changed with the thermal expansion of the shaft of the ball screw mechanism, and thus, a size of the printing plate precursor also changes. When the material of the shaft differs from that of the rotary drum and/or the support of the printing plate precursor, the materials have coefficients of thermal expansion, which are different from each other, and thus, a scale of an image during recording changes, resulting in an improperly formed image.
The recording positions must have no deviations, especially when the image is in color where such deviations become even more noticeable. For example, when colors are recorded on a printing plate precursor (i.e., C (cyan), M (magenta), Y (yellow) and K (black)), the four colors are recorded separately on respective printing plate precursors. Degraded accuracy of registration is thus a large factor in causing image deviations.
When the device is activated at a low temperature (i.e., with no warm-up, hereafter referred to as “cold”), the temperatures of each section in the device tend to differ from each other considerably. Accordingly, another problem arises in that when the device is activated, especially cold, a relative amount of deviation between a position of the ball screw mechanism and that of the printing plate precursor increases, and thus, a difference between a scale change of the ball screw mechanism and that of the printing plate precursor increases, resulting in the accuracy of registration being considerably degraded.